Generally, a unit load device (ULD) is used to carry products by air. ULDs include both aircraft pallets and aircraft containers. During ramp transfers, before or after a flight, products transported in and/or on these ULDs can be exposed for several hours to the outside environment without any added protection. In the case of temperature-sensitive cargo, such as horticultural products, pharmaceutical products, fresh meat and fish, frozen goods and electronics, this period can be detrimental.
Plastic films sometimes used with aircraft pallets do not allow sufficient gas exchange between the load and the outside environment. The horticultural products protected by these plastic films may undergo anaerobic respiration because of the lack of oxygen. Anaerobic respiration results in the development of off-flavors and off-odors (fermentation) and often has non-reversible consequences on the quality attributes of the products.
In addition, to oxygen and carbon dioxide, ethylene is another gas that can have significant effects on the quality of horticultural products. Ethylene is a product of all organic combustion (including engines emissions) but is also a natural hormone endogenously produced by several horticultural products. Ethylene has different effects on horticultural products; some are beneficial and other detrimental (particularly for flowers). For example, ethylene will accelerate and uniformize the ripening process and contribute to the development of aromatic components. However, ethylene also causes the yellowing of green tissues, shortens the shelf life and induces bitter taste. In the case of flowers, ethylene causes leaf fading, wilting and abscission, enrolling of the petals and also failure or earlier closing of the flower buds.
A proper level of relative humidity is often important in order to avoid condensation on the packaging system of the products and/or the products themselves. Condensation often needs to be avoided for several reasons. For packaging systems made of cardboard or other paper based materials (non-waxed) or any hydrophilic materials, condensation may results in an important decrease of their nominal strength and can therefore cause the collapse of the packaging system and mechanical damage to the products. Condensation (or any free water) is also favorable to the growth of decay organisms on horticultural products. In favorable conditions, only a few hours are necessary for mold to develop. Mechanical damage to horticultural products and the presence of free water have a synergic effect on the growth of decay organisms.
Also, high relative humidity levels in the cargo hold of an aircraft are known to affect the reliability of the aircraft smoke detection system and to cause false fire alarms. Consequences of a spurious alarm can be very serious and place passengers and crew members in hazardous situations. False fire alarms result in delays, emergency landings and evacuations causing injuries to number of passengers. In some situations, the pilot may also have to choose between going on with fire alarm on or trying a sea landing. With time, a high number of false fire alarms may result in a lost of confidence of the pilots in the fire detection system and then lead to a real fire warning being ignored. Furthermore, the costs associated with aircraft evacuation emergency procedures, such as triggering of emergency doors and chutes, injuries to passengers, emergency landing fees, and delays are extremely high.